1. Field of the Art
The present invention relates to a vacuum valve controller for a vacuum sewer system in which soil water in a soil water basin is sucked through a suction pipe by opening a vacuum valve and sent to a predetermined place, e.g., a sewage disposal plant.
2. Prior Art
FIG. 5 shows one example of the arrangement of a conventional vacuum sewer system of the type described above. In the figure, reference numeral 10 denotes a soil water basin. One end of a suction pipe 12 is inserted into the soil water basin 10. The other, or rear, end of the suction pipe 12 is connected to a line 15 which communicates with a vacuum tank (vacuum system not shown) through a main valve 14 of a vacuum valve. A vacuum valve body 13 has in a chamber 13c a diaphragm 13b and a spring 13a for biasing the diaphragm 13b into a valve closing position.
Reference numeral 200 denotes a controller for on/off controlling the vacuum valve. The controller 200 has a cylindrical casing 201. The inside of the casing 201 is divided into a sensor chamber 202, a first chamber 203, a second chamber 204, a third chamber 205, a fourth chamber 206, and a fifth chamber 207. The sensor chamber 202 is connected to a pressure sensor pipe 11, which is disposed in the soil water basin 10 through a pipe 208. The fifth chamber 207 is connected to an actuating chamber 13c in the vacuum valve body 13 through a pipe 209. Further, the fifth chamber 207 communicates with the outside air through a breather pipe 210.
The fourth chamber 206 is connected to the line 15 through a pipe 211 and a check valve 212. The first chamber 203 is connected to the breather pipe 210 through a filter 213 and a check valve 214 with an orifice. The second and third chambers 204 and 205 are connected to each other by a pipe 216 through a needle valve 215. The distal end of the pipe 216 is connected to the fourth chamber 206 through a bevel check valve 217.
In the vacuum sewer system arranged as shown in FIG. 5, when the level of soil water Q in the soil water basin 10 is low, and consequently the system is in a stand-by position, the lower end of the pressure sensor pipe 11 lies above the soil water surface. Therefore, the sensor chamber 202 and the first chamber 203 are placed under the atmospheric pressure, and the sensor diaphragm 218 is in a neutral position. Accordingly, the sensor lever 220 closes the air passage 223 by the action of the vacuum in the second chamber 204 and the force of a spring 219, and thus no air flows through the air passage. The vacuum in the pipe 15 is coupled to the third chamber 205 and second chamber 204 through the needle valve 215. Therefore, the two chambers 204 and 205 are placed under the same vacuum. Accordingly, a three-way valve 222 is held in the leftward position by the biasing force of a spring 221. Since the fifth chamber 207 communicates with the atmospheric air through the breather pipe 210, the chamber 13c in the vacuum valve body 13 is placed under the atmospheric pressure. Accordingly, the main valve 14 is pressed in the direction for closing the valve by the spring 13a and thus set in a full-closed state.
As the level of soil water in the soil water basin 10 rises, the pressure detected by the pressure sensor pipe 11 rises. Consequently, the sensor diaphragm 218 moves right-ward and comes in contact with the sensor lever 220. When the pressure exceeds a water column of about 20 mmAq, it overcomes the sum of the force of the spring 219 and the vacuum in the second chamber 204 and causes the sensor lever 220 to separate from the air passage 223. Thus, the air in the first chamber 203 flows into the second chamber 204 through the air passage 223, causing the pressure in the second chamber 204 to rise to a level higher than the pressure in the third chamber 205. When the pressure in the second chamber 204 becomes stronger than the force of the spring 221, a three-way valve driving diaphragm 222a moves rightward, causing the three-way valve 222 to close a hole which communicates with the breather pipe 210. Accordingly, the vacuum in the line 15 is coupled to the chamber 13c in the vacuum valve body 13 through the fourth chamber 206, the axial passage in the three-way valve 222, the fifth chamber 207 and the pipe 209. Thus, the vacuum in the chamber 13c overcomes the force of the spring 13a and raises the main valve 14 from its valve seat, thereby setting the vacuum valve in a fully-open state (i.e., a state where the bore that provides communication between the suction pipe 12 and the line 15 is open).
When the vacuum valve is set in the fully-open state, soil water in the soil water basin 10 is sucked up, and the soil water level begins to fall. The pressure detected by the pressure sensor 11 immediately drops, and consequently the sensor diaphragm 218 moves leftward, thereby allowing the sensor lever 220 to return to the previous position to close the air passage 223. The drop of the vacuum in the line 15 causes the bevel check valve 217 close. Consequently, the second and third chambers 204 and 205 gradually approach the same vacuum through the needle valve 215. As a result, the force of the spring 221 in the third chamber 205 overcomes the pressure in the second chamber 204 and thus causes the three-way valve 222 to move leftward and return to the previous position. Thus, the outside air flows into the fifth chamber 207 through the breather pipe 210, and the air flows into the chamber 13c in the vacuum valve body 13 through the pipe 209, causing the main valve 14 to be closed.
The controller 200, arranged as described above, however, suffers from the following problems:
(1) When the level of soil water Q in the soil water basin 10 falls as a result of suction carried out with the vacuum valve open, the sensor lever 220 closes the air passage 223. The length of time from the instant the air passage 223 is closed by the sensor lever 220 until the second and third chambers 204 and 205 reach the same vacuum, and consequently the main valve 14 is closed, depends on the initial pressure difference between the second and third chambers 204 and 205. Since the pressure in the second chamber 204 is equal to the atmospheric pressure and hence constant, the above-described time depends on the degree of vacuum in the third chamber 205. Consequently, when the degree of vacuum in the third chamber 205 is high, the period of time during which the vacuum valve is open is relatively long; while when the degree of vacuum is low, the period of time is relatively short. That is, when the degree of vacuum in the line 15 is high, the period of time during which the vacuum valve is open is relatively long, and the suction force is also relatively strong. Therefore, a relatively large amount of air is sucked. Conversely, when the degree of vacuum in the line 15 is low, the period of time during which the vacuum valve is open is relatively short, and the suction force is also relatively weak. Accordingly, substantially no air is sucked in. PA1 (2) The gas-liquid ratio, i.e., the proportions in which air and soil water are sucked through the suction pipe 12, depends on the degree of vacuum. That is, when the degree of vacuum is high, the gas-liquid ratio is high; whilst when the degree of vacuum is low, the gas-liquid ratio is low. PA1 (3) When the degree of vacuum is low, the main valve 14 is closed with substantially no air being sucked. Therefore, an air lock is likely to occur in the piping (mainly the line). PA1 (4) Since the control of the gas-liquid ratio is effected by the needle valve 215, which is very small in size, water droplets may close the needle valve 215. If the needle valve 215 is closed by water droplets, the second and third chambers 204 and 205 will not readily reach the same vacuum, and consequently the main valve 14 will not readily be closed. PA1 (5) The controller 200 is installed within an upper space of the soil water basin 10 and, therefore, it must be sealed against entering of the soil water therein. However, the hole communicated with the breather pipe 210 is not positively closed by the three-way valve 222 even when the soil water level in the soil water basin is high. PA1 (6) For a vacuum valve which is disposed close to a vacuum pump station, the gas-liquid ratio should preferably be minimized. However, it is difficult to reduce the gas-liquid ratio when the degree of vacuum is in the ordinary vacuum range of from -0.3 to -0.7 kg/cm.sup.2. That is, since more air is sucked than is needed, the load on the vacuum pump is greatly increased. PA1 (7) The conventional controller requires a large number of components, i.e., a needle valve, a sensor lever and other elements, and has a complicated structure. Therefore, a great deal of time is required for maintenance. PA1 (8) Since a vacuum is used for activating, the operation of the controller and the vacuum valve may become unstable on account of variation in the degree of vacuum.
Thus, basically, the breather pipe 210 must be installed outdoors in order to prevent water or any other liquid from entering the casing of the controller 200.
In view of the above-described circumstances, it is an object of the present invention to provide a vacuum valve controller for a vacuum sewer system, which is free from the above-described disadvantages and which is capable of stably operating with a simplified structure.